Metal-containing polymers are attracting significant interest as these materials may combine the processability and mechanical properties of polymers with the unique optoelectronic properties of metal complexes. The development of metal-containing polymers with unique property profiles has been propelled by their potential use in diverse areas such as solar energy conversion, anti-corrosion, luminescent sensing, electroluminescence display, biotechnology, molecular machines, and molecular electronics. Thus, a number of metal-containing polymers, whose metal moiety is in either the polymer backbone or the side chain, have been reported in the literature. In particular, metal-containing polymers with well-defined architectures are currently under extensive investigation.
As polymerization has been utilized to construct new materials that serve to replace or improve naturally occurring materials, methods have been developed to control the parameters of the chemical processes used to produce the polymers. Control of these permits the preparation of polymers having specific technical requirements. Polymerization thermodynamics and kinetics are well understood and provide a wide array of options for conducting polymerization reactions, i.e., free radical polymerization reactions.
Currently, various polymerization techniques such as atom transfer polymerization (ATRP), ring-opening polymerization (ROP), nitroxide-mediated radical polymerization and reversible addition-fragmentation transfer (RAFT) are used for preparation of metal-containing macromolecules. However, both ATRP and ROP are successful only for a limited number of monomers and suffer from a number of disadvantages such as high reaction temperature and expensive reagents that are sometimes difficult to separate from the products. Moreover, RAFT polymerization can lead to colored polymers with long time consumption. Therefore, conventional free radical polymerization still possesses great potential from an industrial standpoint.
It is well known that an initiator plays an important role in radical polymerization since it determines the polymerization rate, the molecular weight, and other characteristics of polymers. Many ethylenically unsaturated monomers are polymerized by the use of free radical initiators, e.g., those having aliphatic azo or peroxide groups. However, the azo initiator is most commonly used because of its favorable kinetics of decomposition. Particularly, the functionality of the polymer chain ends derived from the used initiator can affect or alter the properties of the polymers.
Most synthetic approaches for the preparation of metal-containing polymers, however, have involved the construction of systems with broad molecular weight distributions and lack of control over polymer architecture. Therefore, it would, therefore, be desirable to provide a compound that is capable of initiating the polymerization of ethylenically unsaturated monomers to produce polymers having ligand terminal groups, which can subsequently complex with metal ions to form supramolecular materials.